1. Field of the Invention
The present invention relates to a nickel-zinc battery.
2. Description of the Related Art
Zinc secondary batteries have been developed and studied over many years. Unfortunately, these batteries have not yet been put into practice. This is due to a problem that zinc contained in the negative electrode forms dendritic crystals, i.e. dendrites, during a charge mode of the battery and the dendrites break the separator to cause short circuit between the negative electrode and the positive electrode. In contrast, nickel-cadmium batteries and nickel-hydrogen batteries have already been commercialized. Nickel-zinc secondary batteries, however, have advantages over such commercialized batteries. In specific, nickel-zinc secondary batteries have a very high theoretical density of capacity; i.e., about five times that of nickel-cadmium secondary batteries, 2.5 times that of nickel-hydrogen secondary batteries, and 1.3 times that of lithium ion batteries. In addition, nickel-zinc secondary batteries are produced from inexpensive raw materials. Thus, a strong demand has arisen for a technique for preventing the short circuit caused by dendritic zinc in zinc secondary batteries.
For example, Patent Document 1 (WO2013/118561) discloses a nickel-zinc secondary battery including a separator composed of a hydroxide-ion-conductive inorganic solid electrolyte between a positive electrode and a negative electrode for preventing the short circuit caused by dendritic zinc, wherein the inorganic solid electrolyte is a layered double hydroxide (LDH) having a basic composition represented by the formula: M2+1−xM3+x(OH)2An−x/n.mH2O (wherein M2+ represents at least one type of divalent cation, M3+ represents at least one type of divalent cation, An− represents an n-valent anion, n is an integer of 1 or more, and x is 0.1 to 0.4).
Sealed nickel-zinc batteries have been disclosed which are provided with negative electrodes that absorb to recycle oxygen gas generated at the end of a charge mode. For example, Patent Document 2 (JPH05-303978A) discloses a sealed nickel-zinc battery including an electrode assembly including a positive electrode plate, a negative electrode plate, a separator, and a retainer, and a liquid-retainable layer disposed around the assembly, wherein the liquid-retainable layer is composed of a fibrous cellulose material having a length of 0.5 to 50 mm and a diameter of 5 to 100 μm and impregnated with an electrolytic solution. The separator used in the battery disclosed in Patent Document 2 is composed of a porous polypropylene membrane treated with a surfactant. Patent Document 3 (JPH06-96795A) discloses a sealed nickel-zinc battery including an electrode assembly, a battery container, and an electrolytic solution, wherein the negative electrode of the assembly faces the bottom of the container, and the electrolytic solution has a volume that is more than 98% and 110% or less of the total spatial volume of the electrode assembly. The separator used in the battery is composed of a microporous film and a cellophane membrane.
A technique has been disclosed for facilitating the permeation of oxygen gas generated from a positive electrode through a separator to a negative electrode during an overcharge mode of a battery. For example, Patent Document 4 (JPH05-36394A) discloses a separator for an alkaline battery, the separator being composed of a porous hydrophobic resin membrane having a surface coated with at least a hydrophilic fabric.